Technical Field
The following disclosure relates to a negative pressure controller configured to control a negative pressure in a vacuum chamber in a vacuum booster.
Description of the Related Art
Patent Document 1 (Japanese Patent Application Publication No. 2013-159241) discloses a negative pressure controller configured to control a negative pressure in a vacuum chamber in a vacuum booster by controlling a vacuum pump connected to the vacuum chamber. This negative pressure controller includes two negative pressure sensors for detecting the negative pressure in the vacuum chamber. A predetermined one of the two negative pressure sensors is selected, and the vacuum pump is controlled based on an output value of the selected negative pressure sensor (see the paragraphs [0029] and [0030]). When an absolute value of a difference between output values of the two sensors is larger than or equal to a failure determination value, it is detected that there is a malfunction in at least one of the sensors (see the paragraph [0038]). It is then determined whether an absolute value of a difference between (i) an estimate value of an amount of change in a pressure (an estimated amount of change) in the case where the vacuum pump is operated and (ii) an amount of actual change in each of the output values of the negative pressure sensors falls within a normal range. It is determined that there is a malfunction in a sensor in which the absolute value of the difference does not fall within the normal range (see the paragraphs [0043]-[0045]). Patent Document 2 (Japanese Patent Application Publication No. 2011-098607) discloses a malfunction detector configured to detect a malfunction in a negative pressure sensor. In the case where an output signal of a negative pressure sensor is to be changed by, e.g., operation of a brake pedal, when the output signal does not change, this malfunction detector detects a malfunction in the negative pressure sensor (see the paragraph [0032]).